Microinjections of opiates into various brain structures revealed that these compounds exert differential effects on motor behaviors depending on site of injection. Opiates and neuroleptics were found to produce catalepsy through different brains structures. Opiates appear to activate the dopaminergic nigro-striatal pathways through some indirect mechanism since iontophoretic applications of morphine to zona compacta neurons failed to influence their spontaneous activity. Opiates appear to produce at least part of their analgesic actions by inhibiting the transmission of pain information through the nucleus giganto-cellularia. Stress-induced analgesia does not appear to be mediated by the release of enkephalin.